This invention relates generally to the testing of components, and more particularly to methods and apparatus for testing components having non-uniform surfaces.
Eddy current (EC) inspection devices are used to detect abnormal indications in a component under test such as, but not limited to, a gas turbine engine component. At least one known EC inspection device is used to detect cracks, pings, dings, raised material, and/or other surface imperfections on a surface of the component, and/or to evaluate material properties of the component including the conductivity, density, and/or degrees of heat treatment of the component.
During operation, known EC devices measure the interaction between an electromagnetic field generated by the EC device and the component being tested. For example, known EC devices include a probe coil that generates a magnetic field. When the coil is positioned adjacent to a conductive component, an eddy current is generated on the surface of the component. A flaw on and/or near the surface of the component generates a disruption in the eddy current field which produces a secondary field that is received by the eddy current probe coil or by a sensor coil in the eddy current probe which converts the altered secondary magnetic field to an electrical signal that may be recorded on a strip chart recorder for example.
While known eddy current inspection techniques are relatively effective at detecting material defects on aircraft engine components, the eddy current inspection device may be affected by a variety of conditions that the probe may encounter while inspecting the component. For example, the eddy current inspection system may generate a relatively uniform signal when the EC inspection system detects a surface crack near a uniform surface region of the component.
However, the EC inspection system may generate a spurious signal when a crack or flaw is detected near the edge of a component that includes relatively complex geometric features. Therefore, it is relatively difficult for an operator to distinguish geometric edge signals generated by the EC device when the EC device is passed over a crack and/or seam at the edge of a component. More specifically, it is often difficult for an operator to distinguish the signals generated from a real crack and/or seam from the spurious signals that may be generated near the edge of a component that has a relatively complex geometry.
As an example, at least one known EC device generates real-time images from identical, repeated geometries in a component, to facilitate improving images that include spurious signals. More specifically, a plurality of images are generated along the surface of the component, wherein each image represents only a portion of the component. After several of these images are collected, a subtraction process is utilized to extract the images from adjacent features. While this method facilitates reducing the dominant edge signals that are common to adjacent features, the method does not eliminate spurious edge signals that are caused by the geometry variations within the component. Accordingly, if only one component feature is to be inspected, the method is less effective because there are no repeated images to subtract.